The purpose of this study is (1) to establish the qualitative and quantitative toxicity of aminopterin in children and adults, (2) to determine the acute dose-limiting toxicities and time(s) to recovery, (3) to determine if there is cumulative toxicity, (4) to establish a maximum-tolerated dose of aminopterin that results in tolerable toxicity which is predictable and reversible and can be used in phase II trials, (5) to determine the minimal amount of leucovorin rescue that is needed to protect from excessive tosicity, and (6) to determine precautions and supportive therapy that should be used.